Such machines are known which consist of self-propelled mobile tanker wagons for the bulk transport of slurry, each wagon having a plurality of tines mounted on a subframe across the back end, and each tine having a slurry injection pipe fixed to its back wall or edge and terminating in a discharge orifice located at a height sufficiently above the level of the working tip of the tine to minimize the risk of clogging by loosened soil. Further anti-clog protection is usually afforded by chamfering or deflecting the discharge orifice so that it faces to the rear in relation to the normal forward travel of the machine.
When slurry is to be disposed below surface level, it is desirable to achieve two objectives. The first is total enclosure of the body of fluid injected, and the second is that it be disposed in as wide and shallow a zone as possible. Total enclosure is primarily an environmental objective, especially where the fluid being buried has a noxious odor or represents a health risk if left exposed on the surface. There is also an economic factor in that absorption by the soil is more efficient if the substance is totally enveloped. Following from this, absorption is more effective if the absorbing zone is wide and shallow so that the maximum surface area is exposed to the action of soil micro-organisms which break down the buried substance, and distribution to plant roots of the fertilizing constituent is more widespread, thus avoiding "banding" of the site by alternate strips of lush and lean vegetation.
Furthermore, any slurry left exposed on the surface is liable to be carried away by surface run-off in wet weather and thus to be a source of pollution of streams and rivers while at the same time representing a loss of valuable nutrients to the burial site. Alternatively, if not washed away by rain, constituents may be lost by ultraviolet degradation or evaporation while the texture of the soil at the surface becomes caked and impenetrable to oxygen.
From this it is apparent that the use of normal cultivating tools is to be avoided, since they are primarily designed to break up soil or even to turn it over by bringing subsoil to the surface. Since many of the best sites for the burial of slurry are natural grasslands whose economic value is as grazing, the need for minimum disturbance of the surface is paramount.
It is known to vibrate conventional cultivating tools to assist in the break-up of the soil. In some cases, this has been achieved by the use of fixed-amplitude vibrators such as crank and link type mechanisms. These are insensitive to the type and consistency of soil being worked and their sole objective is more rapid break-up of the soil. For this reason they are quite unsuitable for the purpose of the present invention. In other cases, free-running vibrators have been proposed which do not dictate the magnitude of the vibratory displacement of the tool. Frequently, however, the vibration imparted has been polar in character, involving a component of angular excitation of the tool. This also is not desirable for the formation of a wide but shallow tunnel below the surface of the soil which is best achieved by purely vertical excitation of the tool.
It has been proposed to achieve purely vertical vibration in a cable-burying machine using a narrow split plough. The plough is in the form of a pair of complementary narrow vertical plates having narrow pointed shoes which together form a tunnel of suitable size to receive a cable. The plates are suspended from a vibrator mechanism so as to move vertically in phase opposition and produce a shearing action on the soil which aids penetration. The plates embrace a guide for feeding the cable into the tunnel. This machine produces exactly the opposite of the objective of the present invention, viz: a wide shallow tunnel.
It has also been proposed to drain grassland by cutting a plurality of grooves thereacross which are immediately filled with sand or like water-pervious material. The tool for this purpose is a narrow blade which has secured to its rear edge a chute for the deposition in the groove cut by the blade of the sand or like drainage material. The blade and attached chute are vibrated in a fore-and-aft mode by a fixed-amplitude crank and link mechanism.